The non-linear properties of iron based magneto-rheological (MR) fluids are investigated at low magnetic field strengths (0 - 1.7 kA/ m) and different gap thickness ( 0 500 mum) in a plate-plate configuration. Single-width chain models qualitatively predict the low-shear flow behavior when plotting the field-specific viscosity, eta(F), as a function of the Mason number, Mn: a slope close to) 1 is observed in log-log representations. Wall depletion effects are observed when the suspensions are sheared under the presence of low external magnetic fields applied and/or large gap distances. These results are correlated to frictional yield stress measurements and chain length distribution calculations in the presence of the external magnetic field. Finally, an equivalent slip layer thickness is calculated using the method of Yoshimura and Prud'homme.